Some thoughts and info on full spectrum lighting, what we do in zoos, ideas for home; what is your experience? Providing the Proper Type and Amount of Light to Pet Birds | That Bird Blog
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
My avian vet said if they don't get exposure to sun (no window or screen in the way) they need a UV light on for 8 hours a day.
Indirect will work just as fine as direct... the rays bounce around, so in the shade, there will still be some amount of UVB/UVA rays getting to you and your birds.
Screen will cut down on the total illumination, by the amount reflected away by the wires in the screen, but it should not single out the UV. The wavelength is so short it's not going to cause diffraction.
Another way to say it is that screen with holes big enough you can see won't alter the spectrum of the light until you get way out the red end, in the infrared. Until the size of the holes/wires and the wavelength of the light become comparable, it's like throwing balls through windows, you don't get effects like diffraction or interference to any significant degree. You can miss the window and bounce back, but as long as the ball is much smaller than the window, the probability of bouncing back isn't affected by the size of the ball.
OTOH, if the wires cover 20% of the area, you'll lose 20% of the light in all wavelengths.